[tox] Update doc testenv to account for documentation restructuring
* Build doc from `doc` directory.
* Use `sphinx-build` directly instead of `make` as this now works and allows
to build within .tox temporary environment (instead of doc/_build),
preferable for a "test" action.
Related to #5447161.
\.svn
^build$
^dist$
\.egg-info$
^.tox$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data.*/database/.*\.sqlite
.*/data.*/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
data/pgdb/
data.*/pgdb.*